I'm done with RRLP!

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Craig Reading craig.reading1 at gmail.com
Mon Apr 8 20:44:47 UTC 2013


PHew! - finally finished my experiments with RRLP. Full details at
www.genesysguru.com

In summary:

range error=ephemURA of xx.0 (xx) doesn't fit in (0,15)

The problem seems to be that SV accuracy in metres is being used as the URA
index. The confusion arises due to differences between the Receiver
Independent Exchange Format (RINEX) 2.10 format and Interface Specification
IS-GPS-200 (http://www.gps.gov/technical/icwg/). IS-GPS-200 section
20.3.3.3.1.3 states: ”SV Accuracy - Bits 13 through 16 of word three shall
give the URA index of the SV. The URA index (N) is an integer in the range
of 0 through 15.”

RRLP server needs to be  modified to support RINEX and specifically to add
a mapping from SV accuracy to URA index. For now I changed line 1084 in
rrlpserver.erl to assume a URA index of 6 e.g. SV accuracy in the range
13.65 – 24 metres:

stuff("ephemURA", nmth(7,1,Tokens), AdjustTable),

Change to:

stuff("ephemURA", “6” , AdjustTable),

With Control.Call.QueryRRLP.Early OpenBTS option configured a crash occurs.

OpenBTS: ../CommonLibs/Vector.h:189: void
Vector<T>::copyToSegment(Vector<T>&, size_t, size_t) const [with T = char,
size_t= unsigned int]: Assertion `base+span<=other.mEnd' failed.

Hence the solution for now is to unconfigure this option:

unconfig Control.Call.QueryRRLP.Early

It looks at though the Almanac file downloaded from
http://www.navcen.uscg.gov/?pageName=currentAlmanac&format=yuma is saved
into /tmp/almanac as HTML rather than plain text:

As a quick fix I changed my Almanac URL:

config GSM.RRLP.ALMANAC.URL
http://celestrak.com/GPS/almanac/Yuma/almanac.yuma.txt

My final configuration options are:

config GSM.RRLP.ACCURACY 40
config GSM.RRLP.ALMANAC.ASSIST.PRESENT 1
config GSM.RRLP.ALMANAC.URL
http://celestrak.com/GPS/almanac/Yuma/almanac.yuma.txt
config GSM.RRLP.EPHEMERIS.ASSIST.COUNT 3
config GSM.RRLP.EPHEMERIS.REFRESH.TIME 0.5
config GSM.RRLP.RESPONSETIME 6

Hope this helps!

I'm moving on to experiments with Uplink-Time Difference of Arrival
(U-TDOA) methods for locating mobile devices with a bit of GSM burst data
analysis , Complex Event Processing (CEP) and data correlation thrown in ….
I call this Mobile Fingerprinting … lets see!

Regards
Craig
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